1. Field of the Invention
The present invention relates to a roll-over alarming device for a crane using a load cell which can endure a maximum load of an outrigger of a crane and measure a low load with high accuracy.
2. Description of the Related Art
A vehicle-mounted crane which is a crane mounted on a vehicle is generally provided with an outrigger, and is adapted to extend the outrigger to be grounded for ensuring stability at the time of a crane operation. However, when a lifted load or operating radius becomes excessive, there is a possibility that the crane loses its balance and rolls over.
Thus, for preventing such a roll-over accident, a roll-over preventing device for a crane has been used which always detects a grounding load of an outrigger in operation and determines a floating condition of the outrigger to issue an alarm when a detected load reaches below a predetermined value (in general, optionally set in a range of 0 to 3000 N).
Conventionally used means for detecting the grounding load of the outrigger of the roll-over preventing device for the crane includes means for detecting an inner pressure of an outrigger cylinder or means for detecting the grounding load using a load cell.
However, the means for detecting the inner pressure of the outrigger cylinder has high frictional resistance of packing of the outrigger cylinder with doubtful accuracy of a detected value and is not fit for use.
The means for detecting the grounding load using the load cell has high detection accuracy when detecting a high load as in the case where the outrigger is in a maximum load condition, but has low detection accuracy when detecting an extremely low load as in the case where a floating condition of the outrigger is detected.
That is, a generally used load cell is selected depending on a value of a maximum measuring load, but a limit load (load capacity) of the load cell is typically on the order of 1.5 times the maximum measuring load. Generally, in the case of load detecting of the outrigger, a maximum load is on the order of 90000 N, thus the load cell with the limit load on the order of 135000 N must be used.
However, as shown in FIG. 20, when the loads of 0 to 3000N are measured by the load cell with the limit load on the order of 135000 N, an output value of the load cell is on the order of 2% of a maximum output value, which is a minute output. Thus, accurate load detection is difficult in view of a measuring error or the like of the load cell itself.
The present invention is directed to solve the above problems in a roll-over alarming device for a crane and has its object to provide a load cell which can endure a maximum load of an outrigger of a crane and detect a low load with high accuracy and a roll-over alarming device with the load cell.
The load cell used for the present invention includes a coil spring provided with a strain gauge, and an upper load cell case and lower load cell case which support the coil spring from its top and bottom to transfer a load of an outrigger to the coil spring, wherein supports, which support the load to restrain yielding of the coil spring when the load having more than a predetermined value acts, are provided between the upper load cell case and lower load cell case.
The load cell has the supports, which support the load as substitutes for the coil spring when the load of an outrigger reaches more than the predetermined value, and thereby has a large load capacity, so that the load cell with a small maximum measuring load may be selected, which provides high detection accuracy of a low load at a low cost.
A roll-over alarming device for a crane according to the present invention, wherein the load cell is mounted on the outrigger of the crane so as to issue a roll-over alarm on the basis of a load detecting value of the load cell, can be manufactured at a low cost and issue a roll-over alarm with high accuracy, thereby improving safety.
The load cell is provided in an outrigger cylinder of a crane so as to vertically move a predetermined distance, and the upper load cell case is mounted on an outer box of the outrigger with a pin, which facilitates mounting of the load cell.
The load cell is configured in a float shape, and the upper load cell case is mounted on an outrigger cylinder with a pin, thus the load cell may be mounted as a substitute for a conventional float, which further facilitates mounting of the load cell.
The roll-over alarming device for a crane, wherein the load cell is configured in such a manner that the load cell integral with an alarming section can be disposed under a float of the outrigger, and the roll-over alarm is issued on the basis of a load detecting value of the load cell, may be disposed under the outrigger cylinder before a start of a crane operation and housed in a housing place when the crane operation is finished, and is not incorporated in the outrigger itself, and thereby can be applied to all the cranes with general versatility.
The load cell and alarming section of the roll-over alarming device can be separately disposed, a radio transmitter for transmitting a load detecting signal is provided on the load cell side, and a radio receiver for receiving a load detecting signal is provided on the alarming section side, thus an operator can recognize the roll-over alarm more reliably in a crane which is operated by the operator apart from an outrigger.